Method of controlling the temperature of the work area of a processing machine and machine tool

ABSTRACT

A method of controlling the temperature of the work area of a processing machine, in particular a machine tool, is proposed, in which exhaust air is removed from the work area and purified and at least a portion of the purified exhaust air is returned to the work area as return air, wherein the temperature of the return air is controlled.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of German Application No. 103 55 277.4, filed Nov. 19, 2003, and German Application No. 10 2004 003 227.0, filed Jan. 22, 2004, which are incorporated herein by reference in their entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a method of controlling the temperature of the work area of a processing machine, in particular a machine tool.

If the temperature in the work area of a processing machine changes too severely during the processing process, this can have effects on the processing method, since the dimensions of a workpiece can change as a result of thermal expansion. Problems can then arise with dimensional accuracy.

SUMMARY OF THE INVENTION

In accordance with the invention, a method of controlling the temperature of the work area of a processing machine and in particular a machine tool is provided, by means of which a simple structure of the processing machine can be achieved.

In accordance with the invention, exhaust air is removed from the work area and purified and at least a portion of the purified exhaust air is returned to the work area as return air, wherein the temperature of the return air is controlled.

Processing products are formed in the work area during the processing of workpieces, wherein during dry processing or during processing using minimal quantity lubrication, in which the method according to the invention may be used particularly advantageously, the processing products are primarily solid materials such as chips and dusts. The exhaust air, which is the gas that forms in the work area and which can be air, for example, is removed with the processing products contained therein and purified. Since exhaust air is removed, supply air must also be supplied. According to the invention, purified exhaust air as return air is used as supply air, wherein a control of the temperature of the work area is performed by means of this return air (which can be a portion of the purified exhaust air or the whole of the purified exhaust air), in that the temperature of the return air, which is fed into the work area, is accordingly open- and/or closed-loop controlled. A substantially constant temperature can then be reached in the work area, which is essentially independent of the time of day and season.

According to the invention, the removal of exhaust air is linked with a temperature control to prevent emissions from the processing machine. This results in a simple structure of the corresponding processing machine, wherein at the same time a high dimensional accuracy may be reached for the processed workpieces. According to the invention, a circulation of exhaust air, at least in partial configuration, is provided in order to achieve a temperature control of the work area jointly with a removal of processing product. In particular, it is provided that the temperature of the return air is adjusted to thus be able to control the inside temperature of the work area with close tolerance limits, for example.

In principle, it is possible that the temperature adjustment of the return air occurs as a result of a temperature adjustment occurring in the exhaust air before purification. It is particularly advantageous if the temperature adjustment of the return air occurs after purification, since the purification itself and the air circulation can be associated with an input of heat.

As a general rule, an input of heat occurs in the processing area as a result of processing operations therein. Therefore, cooling is usually provided in order to control the temperature of the work area. Such a cooling may in turn be achieved if the return air is cooled. By feeding cooled return air into the work area, the input of heat through the processing of a workpiece in the work area can be compensated so that the temperature in the work area may in turn be kept substantially constant in this way.

The temperature of the return air can be controlled simply if the return air is directed through a heat exchanger. For example, the heat exchanger has a heat transfer liquid such as water flowing through it, by means of which a heat transfer to the return air can occur, and in particular cooling of the return air can occur.

It is beneficial if the temperature of the return air is measured before passage through the heat exchanger and additionally the temperature of the return air is measured after passage through the heat exchanger. This enables the cooling performance (or the heating performance in the case of heating) of the heat exchanger to be determined and checked accordingly. In particular, the temperature of the return air is adjusted via the heat exchanger for feeding into the work area to thus allow the temperature of the work area to be controlled.

It is most particularly advantageous if exhaust air is conducted in a loop. As a result of this, the emissions of the processing machine are minimized and the temperature of the work area can be controlled. In this case, the loop can be closed or open.

It is beneficial if the loop has one or more outlets. This allows gas and exhaust air in particular to exit the loop. This is necessary, for example, if ambient air is fed into the system to provide an additional control possibility. For the same reason, it is beneficial if the loop has one or more inlets, so that gas, for example, and ambient air in particular can feed externally into the system. In this case, an inlet can be provided at the work area. Via this inlet gas such as ambient air, for example, can then feed directly into the work area in order to achieve a temperature control of the work area with the aid of this gas feed.

It is most particularly advantageous if return air is introduced into the work area above the discharge of exhaust air in relation to the direction of gravity. This enables processing products to be removed, wherein the turbulence as a result of the flow path is minimized.

It is most particularly advantageous if return air is fed into the work area in such a manner that a downwardly directed flow can form at work area walls. As a result of this, a kind of gas cushion, which prevents contamination and the deposit of processing products, can form on the work area walls subjected to the corresponding flow. This in turn provides better fire protection, for example, since fine dusts above all pose a fire risk.

It is advantageously provided that the temperature is measured in the work area. Deviations from a desired or adjusted predetermined temperature can then be detected and corresponding correcting variables can be changed in a controlled system in order to reach the desired temperature value again. Thus, a control loop can be formed, via which the temperature in the work area may be predetermined with a high degree of constancy.

Alternatively or additionally, it can also be provided that the temperature at the workpiece is measured and/or the temperature of the workpiece is measured. For example, the temperature is measured at a workpiece holder or directly via a corresponding sensor on the workpiece. This also enables a control loop to be formed, if this temperature is used as controlled variable. It can also be provided that the temperature is measured at the processing machine (e.g., at a machine bed).

It is additionally beneficial if the ambient temperature is measured, particularly in the surrounding area of the machine. Variations can occur in the ambient temperature, which can fundamentally influence the work area temperature. For example, a corresponding processing machine in a machine workshop can be set up in the vicinity of an entrance to the machine workshop. This can lead to temperature variations above all in winter. Through the measurement of the ambient temperature such temperature variations can be taken into consideration in a control loop to be able to maintain constant temperatures in the work area as far as possible despite these variations.

It is particularly beneficial if the gas circulation of the work area is controlled with temperature adjustment of the return air. Usually, the circulation performance for the exhaust air does not need to be controlled; this is determined by the geometry of the work area, by its tightness with respect to the environment and by the processing operations of the workpieces themselves. If the control is based on the temperature adjustment, then an optimized temperature control of the work area may be achieved with these predetermined conditions.

It is most particularly advantageous if the control variable is the work area temperature and/or the workpiece temperature. Temperature changes can have a detrimental effect on the dimensional accuracy of a processing operation or a processed workpiece. If care is taken that the corresponding temperature, which can influence this dimensional accuracy, is controlled and in particular controlled to constancy, then workpieces can be processed with high accuracy or the processed workpieces have a high accuracy with close production tolerances.

The temperature of a workpiece to be processed can also be subjected to control.

The control of the exhaust air circulation in particular with respect to the temperature of the return air is performed on the basis of at least one of the variables of temperature of the purified exhaust air and outside temperature.

It is beneficial if ambient air is fed in where needed and, in this case, fed into the work area or at a different location into the exhaust air conduit. For example, it can be advantageous in the case of sharply changing temperature profiles to feed ambient air into the system while at the same time reducing the return air component current. This allows better stabilization of the work area temperature.

In particular it is provided that exhaust air is sucked out of the work area to be able to remove processing products with a corresponding large gas throughput and in particular air throughput through the work area. This extraction by suction is advantageously coupled with a corresponding flow path of the gas in the work area and from the work area.

It can be provided that exhaust air is directed through at least one filter for purification. This is described in DE 201 10 152.1, to which reference is expressly made.

In this case, it can be provided that the return air purification process is conducted in multiple stages. For example, a stage for the separation of chips from the exhaust air is provided, this being a coarse cleaning stage. One or more fine cleaning stages can follow to separate dusts from the exhaust air, for example.

The method according to the invention can be advantageously used if, in the work area, a dry processing method and/or a processing method using minimal quantity lubrication is performed. Then, essentially only solid materials are produced as processing products.

It is most particularly advantageous if the temperature of a workpiece is controlled before processing. As a result, the workpiece is already at a defined temperature at the start of the processing, wherein working from the temperature management a temperature control can be performed in the work area. There is no need to wait until the workpiece has taken on the inside temperature in the work area. This is particularly advantageous if a dry processing is performed, since the heat transfer from air onto the workpiece is poorer than from a liquid onto the workpiece. As a result, waiting times for temperature control of the workpiece in the work area are minimized.

It is most particularly advantageous if the temperature of a workpiece is controlled outside the work area and the workpiece is then transported into the work area. With the temperature control to a suitable temperature, the processing can be started after transport into the work area without waiting times arising with respect to temperature control of the workpiece in the work area.

The invention additionally relates to a machine tool with a work area, in which workpieces can be processed, and with a cleaning device for purifying exhaust air from the work area. Such a machine tool is provided which operates optimally. In accordance with the invention, between the cleaning device and the work area a conduit for return air is arranged, via which the purified exhaust air may be directed into the work area. This enables an exhaust air circulation to form, via which at least a component current of purified exhaust air can be returned into the work area. A temperature control of the work area can be achieved via this exhaust air circulation, if the temperature of the return air is controlled accordingly.

The machine tool according to the invention has the advantages already described in association with the method according to the invention. Further advantageous configurations have also already been explained in association with the method according to the invention.

In particular, the conduit for return air is coupled to a heat exchanger, via which the temperature of the return air, which can be fed into the work area, is adjustable. This enables a control loop to be formed, via which the temperature of the work area, for example, can be controlled to constancy. This in turn allows processing processes to be performed with high dimensional accuracy.

It is then also beneficial if a branching device is provided, via which a component current of the purified exhaust air can be fed to the work area as return air. As a result, it is possible, for example, if gas such as ambient air is additionally fed into an open loop, to control the quantity of return air directed into the work area accordingly so that the extraction performance for exhaust air does not have to be changed.

It is most particularly advantageous if a control device is provided, by means of which the work area temperature can be open- and/or closed-loop controlled. Then, stable temperature conditions can be achieved in the work area within a narrow range of deviation, so that no substantial changes in workpiece dimensions occur as a result of thermal expansion during the processing of workpieces. This in turn enables a high dimensional accuracy to be achieved with respect to the finished workpieces.

It is beneficial if a temperature control device such as a workpiece magazine, for example, is provided, in which the temperature of one or more workpieces can be controlled. This enables workpieces to be processed to be brought to a defined temperature so that the processing operation can be performed on workpieces, which have already reached a desired temperature. In particular, there is then no need for a processing operation to wait until a workpiece in the work area reaches an output temperature for the processing operation.

It is beneficial if a transport section or path is provided for transporting workpieces into the work area. Then, workpieces can be brought to a desired defined temperature in the temperature control device, which is arranged outside the work area, and brought via the transport section or path into the work area.

The following description of a preferred embodiment in association with the drawing serves to explain the invention in more detail.

BRIEF DESCRIPTION OF THE DRAWING

Preferred exemplary embodiments of the invention are explained in more detail hereinbelow with reference to a schematic drawing, in which the single FIG. 1 shows a schematic block diagram of an embodiment of a machine tool according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

An embodiment of a processing machine (such as a machine tool, for example) according to the invention, which is shown in its entirety in FIG. 1 and given the reference 10 therein, comprises a work area 12, in which processing processes of one or more workpieces 14 are conducted. The machine tool can be a single-spindle or a multiple-spindle device. In particular the processing methods are dry processing methods including quasi-dry processing methods or processing methods using minimal quantity lubrication. For example, the lubricant on a tool has a flow rate of less than 150 ml per process hour.

The workpiece 14 can be processed via a tool 16, the tool 16 being positioned in the work area 12 and, for example, movably directed in the work area 12. It can also be fixedly arranged there. In addition or alternatively thereto, the workpiece 14 can also be movably arranged in the work area 12 via a corresponding holder.

During processing of a workpiece 14 processing products are formed, wherein chips and dusts form during the cutting process. The processing of the workpiece 14 in the work area 12 usually takes place in air as work area gas.

However, it is also fundamentally possible for the processing to take place in an inert gas atmosphere, if processing processes are conducted that are oxygen-critical, for example, with respect to explosion risk.

It is provided according to the invention that exhaust air is removed from the work area 12. The exhaust air in this case is composed of work area gas, which is usually air (but is not restricted to air), and processing products such as chips and dust. This exhaust air is extracted by suction, for which purpose a pump 18 can be provided, for example. For this, the work area 12 has one or more outlets 20 for exhaust air, wherein such outlets are formed, for example, via slots in a cladding 22 surrounding the work area 12. This cladding 22, in which the work area 12 is formed, is of gastight configuration in this case.

To the outlet or outlets 20 an exhaust air conduit 24 is coupled, wherein this conduit 24 comprises one or more pipes 26, which are directed to a cleaning device 28. The pump 18 can be a component of this cleaning device 28 to ensure that exhaust air can be transported with processing products as free from interference as possible from the work area 12 to the cleaning device 28.

The exhaust air is purified with the processing products in the cleaning device 28. For purification, the (contaminated) exhaust air passes through one or more filters 30, 32. The cleaning device 28 is preferably of multi-stage configuration and comprises at least one coarse cleaning stage 34 for the separation of cuttings from the exhaust air and a fine cleaning stage 36 for the separation of dusts and suchlike from the coarsely cleaned exhaust air.

Processing products, and particularly chips, separated in the coarse cleaning stage 34 are collected in one or more collection tanks 38. Processing products, and in particular fine dusts, separated in the fine cleaning stage 36 are stored in one or more collection tanks 40.

A cleaning device of this type is described in the German Utility Model No. 201 10 152.1, filed Jun. 21, 2001. The described cleaning device, which serves to separate solid materials from a gaseous medium, i.e., for the separation of processing products from the exhaust air, therein comprises a fine filter provided in a filter housing, such as filter 32, for example, and a detachably connected collecting vessel, such as the collection tank 40, for example. In this case, this collecting vessel can at the same time be a storage container for additives, which can be directed into the filter housing for the filter 32.

The filter housing has a cyclone separator as coarse cleaning stage 34 connected upstream of it. An extraction fan is connected in flow downstream of the filter housing, wherein an air separator is arranged in the flow between the cyclone and filter housing and configured in such a manner that heavier solid materials separated by the cyclone can be directed into the air separator and a predeterminable proportion of these solid materials can be directed through the air separator and then on into the filter housing. In particular, these structural components are combined to form a compact device in respect of structural parts. Reference is expressly made to the above-mentioned Utility Model DE 201 10 152.1. Corresponding cleaning devices are also known under the designation HANDTE dry filters.

The cleaning device 28 has an outlet 42 for purified exhaust air, wherein exhaust air, which is purified essentially from the processing products, can be discharged at this outlet 42. This outlet 42 is coupled via a pipe 44 to an inlet 46 of a branching device 48. This branching device 48 has a first outlet 50, via which purified exhaust air can be discharged from the system and, for example, output to the atmosphere. In addition, the branching device 48 comprises a second outlet 52, via which a component current of purified exhaust air can be discharged. This second outlet 52 is coupled via a pipe 54 to an inlet 56 of the work area 12 for purified exhaust air.

Via the second outlet 52, purified exhaust air can then be fed through the pipe 54 into the work area 12 as return air. As a result, an exhaust air loop 58 is formed, by means of which exhaust air can be circulated between the outlet or outlets 20 of the work area 12 for exhaust air contaminated with solid materials and the inlet or inlets 56 for purified exhaust air (return air).

In this case, it is preferably provided that the inlet or inlets 56 for return air are arranged at the work area 12 above the outlet or outlets 20 for exhaust air in relation to the direction of gravity. The flow path of the corresponding work area gas such as air, for example, in the work area 12 is such that the processing products produced during the dry processing such as chips and dust are taken up by the exhaust air flow in the work area 12 and can be fed to the cleaning device 28. It is provided in particular that the return air/exhaust air is directed downwards from above (in relation to the direction of gravity) at walls 60 of the work area 12, so that a kind of gas cushion can be formed on these walls. The degree of contamination in the work area is reduced as a result. The deposit of solid materials in the work area is also prevented or at least reduced.

It is provided according to the invention that the return air, which is fed into the work area 12, is subjected to (open- and/or closed-loop) control with respect to its temperature. The processing of a workpiece 14 in the work area 12 is usually associated with an input of heat into the work area 12. Moreover, the purification of the exhaust air in the cleaning device 28 can be associated with an input of heat. Therefore, it is generally necessary for the return air to be cooled before being fed into the work area 12.

At least one heat exchanger 62, which is coupled to the pipe 54, is provided for the control of the temperature of the return air. Return air in the form of purified exhaust air flows through this heat exchanger 62, wherein a specific temperature of the return air is adjustable via a heat transfer medium such as water, for example, said return air leaving the heat exchanger 62 at an outlet 64. The outlet 64 in turn is in fluidic connection with the inlet 56 of the work area 12. A liquid conduit for the heat transfer medium is indicated by the reference 66 in FIG. 1.

The extraction performance for the exhaust air is dependent in particular on the geometric configuration of the work area 12, the gas-tightness of the cladding 22 and the type of processing process in the work area 12. It is provided according to the invention that the temperature of the work area 12 is controlled. It is advantageous if the work area is kept at a specific constant temperature (with slight deviations around this predetermined temperature), so that during a processing operation, for example, the dimensions of the workpiece do not change as a result of heat expansion. Control of the work area temperature can be achieved by means of the control of the temperature of the return air, as a result of which it is in turn possible, for example, to keep the work area temperature constant within close tolerances.

For this, a control device 68 is provided in accordance with the invention, which is integrated into the control unit of the machine tool 10, for example. A temperature sensor 70 measures the temperature in the work area 12 and forwards the corresponding measurement signal to the device 68.

In addition, the temperature of the return air is measured before passing through the heat exchanger 62 via a temperature sensor 72. A further temperature sensor 74 measures the temperature of the return air after it has left the heat exchanger 62. The temperature sensors 72 and 74 forward their corresponding measurement signals to the control device 68. This can determine a temperature gradient in the return air conduit with respect to an inlet of the heat exchanger 62 and an output of the heat exchanger 62.

In addition, it can also be provided that an ambient temperature at the machine tool is measured by means of a temperature sensor 76. Moreover, it can also be provided that the temperature at the workpiece 14 is measured via a temperature sensor 78. The temperature sensors 76, 78 also forward their signals to the control device 68.

Further, a temperature control device 84 is provided, in which the temperature of workpieces can be controlled. Workpieces 86 that have been accordingly temperature-controlled can be brought into the work area 12 via a transport section 86. One workpiece or several workpieces can be brought to a defined temperature in the temperature control device 84, so that workpieces can be fed to the work area 12 which have a defined (output) temperature. The temperature control device 84 can be formed, for example, by a workpiece magazine, which can be temperature-controlled, or by a temperature controlling section or path.

The method according to the invention for controlling the temperature of the work area 12 functions as explained below. For example, the inside temperature of the work area 12, measured via the temperature sensor 70, is used as control variable, i.e. as the variable that is to be controlled. The temperature in the work area 12 during processing processes determines the temperature of the workpiece 14. Alternatively, the temperature of the workpiece 14, measured via the temperature sensor 78, can itself be used as control variable.

The temperature in the work area interior is predetermined with close tolerances, e.g., a deviation of 1 K at maximum from the work area temperature to be firmly maintained is tolerated. The temperature sensor 70 measures the current values and forwards them to the (open- and/or closed-loop) control device 68.

The exhaust air is sucked out of the work area 12 with the processing products, i.e. with the solid materials produced, and fed to the cleaning device 28 and purified there. A temperature of the return air is adjusted via the heat exchanger 62 and in that case in particular via a flow rate of liquid through the heat exchanger 62 adjusted by means of a flow governor 80. This flow governor 80 is connected to the control device 68, which can control the flow rate accordingly. The flow of liquid through the heat exchanger 62 is selected so that a specific temperature is set in the return air, which is fed into the work area 12, wherein this temperature is measured by means of the temperature sensor 74. The temperature is controlled as correcting variable or actuating variable so that the controlled variable work area inside temperature remains substantially constant.

The work area inside temperature is also influenced by the ambient temperature, which is measured by the temperature sensor 76. The work area inside temperature can take into account changes in the ambient temperature. By measuring the ambient temperature and taking into consideration during control of the heat exchanger 62, a constancy of the work area inside temperature can also be reached with high accuracy in the case of variations in the ambient temperature.

The cooling performance of the heat exchanger 62 can be determined by measuring the temperature of the return air before the heat exchanger (temperature sensor 72) and after the heat exchanger 62 (temperature sensor 74). The temperature of the return air after leaving the heat exchanger 62 itself can be a secondary control variable to allow the work area inside temperature to be controlled.

The first outlet 50 of the branching device 48 constitutes an outlet of the exhaust air loop 58. As this (purified) exhaust air can leave the system; the exhaust air loop is then an open loop.

One or more inlets can also be provided, via which work area gas and in particular air can be fed into the exhaust air loop 58. For example, an inlet 82 is provided at the work area 12, via which ambient air can be fed into the work area 12. The inlet 82 is controllable in particular in this case, so that it can be opened and closed and the gas feed quantity is preferably also controllable. In particular in the case of sharply changing temperature profiles, there is the possibility therein of influencing the temperature in the work area 12 via additional ambient air. To avoid having to increase the extraction performance, a corresponding reduced component current of return air is then fed into the work area 12.

The quantity of gas introduced via the inlet 82 and in particular introduced ambient air is then an actuating variable or correcting variable, wherein this quantity is controlled by the control device 68. Accordingly, the control device 68 then controls the branching device 48 in order to generate a corresponding component current of return air, which is fed into the work area 12 via the inlet 56. A corresponding inlet for ambient air can also be arranged on the pipe 54 before or after the heat exchanger 62.

Through the initial temperature of the workpieces in the workpiece magazine 84, it is ensured that workpieces are positioned in the work area with a defined temperature. As a result of this, there is in turn no need to wait until the workpiece reaches the desired temperature in the work area 12, if the workpiece has already been heated (or cooled if necessary) accordingly to the desired temperature beforehand. Further, in the case of dry processing there is likewise no need to wait until the workpiece reaches the required temperature in the work area 12, since it was already at the required temperature when brought into the work area 12.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A method of controlling the temperature of the work area of a processing machine, in particular a machine tool, comprising: removing exhaust air from the work area; purifying said removed exhaust air; and returning at least a portion of the purified exhaust air to the work area as return air; wherein the temperature of the return air is controlled.
 2. The method according to claim 1, wherein the temperature of the return air is adjusted.
 3. The method according to claim 2, wherein the temperature adjustment of the return air occurs after purification.
 4. The method according to claim 1, wherein the return air is cooled.
 5. The method according to claim 1, wherein the return air is fed through a heat exchanger.
 6. The method according to claim 5, wherein the temperature of the return air is measured before passage through the heat exchanger.
 7. The method according to claim 5, wherein the temperature of the return air is measured after passage through the heat exchanger.
 8. The method according to claim 5, wherein the temperature of the return air is measured by means of the heat exchanger for feeding into the work area.
 9. The method according to claim 1, wherein the exhaust air is conducted in a loop.
 10. The method according to claim 9, wherein the loop has one or more outlets.
 11. The method according to claim 9, wherein the loop has one or more inlets.
 12. The method according to claim 11, wherein an inlet is provided at the work area.
 13. The method according to claim 1, wherein return air is introduced into the work area above the discharge of exhaust air in relation to the direction of gravity.
 14. The method according to claim 13, wherein return air is fed into the work area in such a manner that a downwardly directed flow can form at work area walls.
 15. The method according to claim 1, wherein the temperature is measured in the work area.
 16. The method according to claim 1, wherein at least one of the temperature at the workpiece and the temperature of the workpiece is measured.
 17. The method according to claim 1, wherein the temperature is measured at the processing machine.
 18. The method according to claim 1, wherein the ambient temperature is measured.
 19. The method according to claim 1, wherein the gas circulation of the work area is controlled with temperature adjustment of the return air.
 20. The method according to claim 1, wherein a control variable is at least one of the work area temperature and the workpiece temperature.
 21. The method according to claim 1, wherein the temperature in the work area is controlled.
 22. The method according to claim 1, wherein the temperature of a workpiece to be processed is controlled.
 23. The method according to claim 19, wherein the control is performed on the basis of at least one of the variables of temperature of the purified exhaust air upon feeding into the work area and outside temperature.
 24. The method according to claim 1, wherein ambient air is fed in where needed.
 25. The method according to claim 1, wherein exhaust air is sucked out of the work area.
 26. The method according to claim 1, wherein exhaust air is fed through at least one filter for purification.
 27. The method according to claim 1, wherein the return air purification process is conducted in multiple stages.
 28. The method according to claim 27, wherein the purification process comprises a stage for the separation of chips from the exhaust air.
 29. The method according to claim 27, wherein the purification process comprises a stage for the separation of dusts from the exhaust air.
 30. The method according to claim 1, wherein, in the work area, at least one of a dry processing method and a processing method using minimal quantity lubrication is performed on workpieces.
 31. The method according to claim 1, wherein the temperature of a workpiece is controlled before processing.
 32. The method according to claim 31, wherein the temperature of a workpiece is controlled outside the work area and the workpiece is then transported into the work area.
 33. A machine tool, comprising: a work area, in which workpieces are processable; and a cleaning device for purifying exhaust air from the work area; wherein, between the cleaning device and the work area, a conduit for return air is arranged via which the purified exhaust air is feedable into the work area.
 34. The machine tool according to claim 33, wherein the conduit for return air is coupled to a heat exchanger, by means of which the temperature of the return air, which is feedable into the work area, is adjustable.
 35. The machine tool according to claim 33, wherein a branching device is provided, via which a component current of the purified exhaust air is feedable to the work area as return air.
 36. The machine tool according to claim 33, wherein a control device is provided, by means of which the work area temperature is controllable.
 37. The machine tool according to claim 33, wherein a temperature control device is provided, via which the temperature of one or more workpieces is controllable.
 38. The machine tool according to claim 37, wherein a transport path is provided for transporting workpieces into the work area. 